Power driven wrenches for assembling and disassembling lengths of threaded pipe have long been known. See, for example, U.S. Pat. No. 2,400,712 issued May 21, 1946 to Prather et al, U.S. Pat. No. 2,746,329 issued May 22, 1956 to W. W. Paget, U.S. Pat. No. 2,576,509 issued July 21, 1970 to Donald C. Duke et al, and U.S. Pat. No. 3,774,481 issued Nov. 27, 1973 to Earl H. Goodman. The tightening and loosening of the threaded connections of pipe lengths often requires the application of considerable torque to the pipe. For this reason the use of a powered wrench greatly facilitates the assembling and disassembling of lengths of pipe.
The requirement for the application of a considerable amount of torque presents a problem in gripping the pipe to be turned tightly enough to prevent relative movement between the pipe and the wrench. The prior art accomplishes this by the use of a hydraulic motor, mechanical linkage, and by a chain wrapped in serpentine fashion about the pipe and the driving means. While some of the prior art devices for rotating a pipe while preventing relative movement between the pipe and the wrench effectively accomplish their intended purpose, many of them result in cumbersome pieces of apparatus which require considerable labor and time to assemble about the pipe. Other prior art provides means to quickly position a pipe against driven rollers of a wrench but is not reliably effective to prevent relative movement between the pipe and the wrench.
Many of the prior art wrenches that effectively grip the pipe to prevent relative movement between the pipe and the wrench undesirably scar the surface of the pipe during its rotation because of the force with which the driven wheels engage and bite into the pipe to perform the desired function of rotating the pipe.